1. Field of the Invention
The present invention relates to a caliper parking brake, and more particularly, a caliper parking brake in which a returning force of a piston that returns to a position before brake when brake is released according to a strength of a brake pressure applied to a brake force output terminal increases so that drag that occurs in a brake disc due to non-return of a frictional pad pressurized by the piston can be removed or reduced.
2. Description of the Related Art
In general, caliper-type parking brakes are brakes that perform a brake operation by pressurizing and stopping a brake disc interposed between a piston and a frictional pad of a fork with a brake force applied to the piston, wherein a rotatative force of a brake lever that rotates by a parking cable during the brake operation is switched to a straight motion, thus generating the brake force of the piston.
In this case, caliper parking brakes can be classified in various manners according to a method of switching a rotatative motion of the brake lever to the straight motion. Thus, representative examples thereof may be ball in ramp (BIR) type caliper parking brakes.
In BIR type caliper parking brakes, uneven parts are formed on matching planes between an input ramp that rotates in synchronization with rotation of the brake lever and an output ramp that is installed to correspond to the input ramp, and a ball or roller is interposed between the matching planes so that, when the input ramp rotates, movement of the ball or roller that moves forward and backward according to rotation of uneven surfaces is transmitted to the output ramp without any change and a rotatative motion of the input ramp is switched to a straight motion of the output ramp, thus generating a brake force.
Meanwhile, in the above-described BIR type caliper parking brake according to the related art, when brake is performed, a piston 103 moves forward within a cylinder 101 and pressurizes a frictional pad 105 against a brake disc, as illustrated in FIG. 1. Thus, in this case, a sealing ring 107 that is closely adhered to an outer circumferential surface of the piston 103 is pushed along the piston 103 and thus is deformed. Thus, when brake is released, the deformed sealing ring 107 is restored to its original shape by its elastic restoring force, and in this procedure, the piston 103 that is closely adhered to the sealing ring 107 is returned to its original position.
However, in the BIR type caliper parking brake according to the related art in which, when brake is released, the sealing ring 10 is returned to its original position by its elasticity, even when a strong brake force is exerted on the piston 103, the sealing ring 107 is excessively deformed and loses part of a restoring force and thus brake is released, the piston 103 cannot be returned to its original position. As a result, quick return of the frictional pad 105 is disturbed, and although brake has been released, the frictional pad 105 and the brake disc are maintained in a contact state, which results in drag.
In addition, when abrasion occurs in the frictional pad 105 due to friction with the brake disc, in an initial stage of brake in which the piston 105 moves forward and starts pressurizing the frictional pad 105, the frictional pad 105 does not contact the brake disc so that substantial brake is not performed, and even in maximum pressure brake in which the piston moves forward to the maximum and pressurizes the frictional pad 105 against the brake disc to the maximum, a brake defect in which a brake pressure does not substantially reach a maximum pressure, occurs.